This work focusses on the use of ultrasonic waves in the mechanical characterization, manipulation, and separation of biomaterials. Initally we are focussing on the elastic properties of red blood cells. Our apparatus levitates red blood cells in an appropriate solution by balancing the force of gravity by an acoustic force which exists because of the scattering of sound by the object in an acoustic standing wave. By comparing the conditions (e.g. voltage input to a transducer) required to levitate the sample at a given position, with the conditions required to levitate a reference material at the same position, we are able to deduce the sample's average compressibility. Two apparatuses exist. One, which operates in the 200-600 kHz range, considers large numbers of cells; another apparatus, which operates from 1-4 MHz, is mounted on the stage of an optical microscope and allows for the manipulation with sound of small numbers or individual cells. The former apparatus has provided quantitative estimates of rbc compressibility which are being compared with estimates based on other techniques.